RSSI estimation in multi-technology communication terminals

ABSTRACT

A method used in a receiver includes measuring first Received Signal Strength Indications (RSSIs) in respective first communication channels, which are located in a given frequency band and which each have a first channel bandwidth. Based on the first RSSIs, second RSSIs are computed for respective second communication channels, which are located in the given frequency band and which each have a second channel bandwidth that is larger than the first channel bandwidth. At least one of the first and second communication channels over which to receive signals at the receiver are selected using the first and second RSSIs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/853,339, filed Aug. 10, 2010, which claims the benefit of U.S.Provisional Patent Application 61/266,448, filed Dec. 3, 2009. Thedisclosures of these related applications are incorporated herein byreference.

FIELD OF THE DISCLOSURE

The present invention relates generally to communication systems, andparticularly to methods and systems for determining received signalstrength and selecting networks in wireless receivers.

BACKGROUND

Wireless communication standards typically define a set of communicationchannels over which transmitters and receivers are to communicate. Inparticular, communication standards typically specify the frequenciesand bandwidths of the communication channels. For example, the ThirdGeneration Partnership Project (3GPP) specifies the communicationchannels for Universal Mobile Telecommunications System (UMTS) networks,in “3^(rd) Generation Partnership Project—Technical Specification GroupRadio Access Network—User Equipment (UE) Radio Transmission andReception (FDD) (Release 9),” TS 25.101, version 9.3.0, March, 2010,section 5.2, which is incorporated herein by reference. The set ofcommunication channels for Global System for Mobile communication (GSM)networks is specified in “3^(rd) Generation PartnershipProject—Technical Specification Group GSM/EDGE—Radio AccessNetwork—Radio Transmission and Reception (Release 9),” TS 45.005,version 8.8.0, March, 2010, section 2, which is incorporated herein byreference. In some cases, frequency bands that are used by differentRadio Access Technologies (RATs) overlap one another.

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

SUMMARY

An embodiment that is described herein provides a method used in areceiver. The method includes measuring first Received Signal StrengthIndications (RSSIs) in respective first communication channels, whichare located in a given frequency band and which each have a firstchannel bandwidth. Based on the first RSSIs, second RSSIs are computedfor respective second communication channels, which are located in thegiven frequency band and which each have a second channel bandwidth thatis larger than the first channel bandwidth. At least one of the firstand second communication channels over which to receive signals at thereceiver are selected using the first and second RSSIs.

In some embodiments, measuring the first RSSIs includes measuring signalstrengths of the signals received over at least one of the firstcommunication channels in accordance with a first Radio AccessTechnology (RAT), and the second communication channels correspond to asecond RAT, different from the first RAT. In an embodiment, only one ofthe first and second RATs is active when the first RSSIs are measured,and selecting the at least one of the first and second communicationchannels includes identifying the active RAT.

In a disclosed embodiment, the method includes initiating communicationwith a base station of the identified active RAT in response toidentifying the active RAT. In another embodiment, measuring the signalstrengths includes receiving the signals of a Global System for Mobilecommunication (GSM) RAT, and computing the second RSSIs includescomputing the second RSSIs in accordance with a Universal MobileTelecommunications System (UMTS) RAT.

In yet another embodiment, computing the second RSSIs includescalculating a second RSSI for a respective second communication channelby summing the first RSSIs measured on a subset of the firstcommunication channels overlapping the second communication channel. Inan embodiment, summing the first RSSIs includes assigning respectiveweights to the first RSSIs in the subset, and summing the weighted firstRSSIs. In another embodiment, summing the first RSSIs includesmultiplying a sum of the first RSSIs in the subset by a factor thatdepends on respective first and second channel filter shapes of thefirst and second communication channels. In an embodiment, the receiverincludes first and second reception circuitry for receiving the firstand second communication channels, respectively, and the method includesdeactivating the second reception circuitry during measurement of thefirst RSSIs.

There is additionally provided, in accordance with an embodiment that isdescribed herein, a receiver that includes reception circuitry andprocessing circuitry. The reception circuitry is configured to receivefirst communication channels that are located in a given frequency band,each of the first communication channels having a first channelbandwidth, and to receive second communication channels that are locatedin the given frequency band, each of the second communication channelshaving a second channel bandwidth that is larger than the first channelbandwidth. The processing circuitry is configured to measure firstReceived Signal Strength Indications (RSSIs) in the respective firstcommunication channels, to compute, based on the first RSSIs, secondRSSIs for the respective second communication channels, and to select,using the first and second RSSIs, at least one of the first and secondcommunication channels over which to receive signals at the receiver. Inan embodiment, a mobile communication terminal includes the disclosedreceiver. In another embodiment, a chipset for processing signals in amobile communication terminal includes the disclosed receiver.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that schematically illustrates amulti-technology wireless communication terminal, in accordance with anembodiment of the present disclosure; and

FIG. 2 is a flow chart that schematically illustrates a method forcommunication in a multi-technology wireless communication terminal, inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments that are described herein provide improved methods anddevices for operating multi-technology receivers. In particular, thesemethods and devices are concerned with receivers that support two ormore Radio Access Technologies (RATs), whose respective frequency bandshave at least partial overlap.

In some embodiments, a receiver supports a first RAT that operates infirst communication channels and a second RAT that operates in secondcommunication channels. Each of the first communication channels has afirst bandwidth, and each of the second communication channels has asecond bandwidth, larger than the first bandwidth. The firstcommunication channels overlap the second communication channels, atleast in a given frequency band. In an example embodiment, the receiversupports both Wideband Code-Division Multiple Access (WCDMA) and GSM inthe same frequency band. In accordance with current standards, eachWCDMA channel has a bandwidth of approximately 4.2 MHz, and each GSMchannel has a bandwidth of approximately 200 KHz.

In some scenarios, the receiver receives downlink signals according toone of the RATs (referred to as “active RAT”), but has no a-prioriinformation as to the identity of the active RAT. For example, when thereceiver initially attempts to join a communication network, itsometimes has no information whether to expect signals in accordancewith the first RAT or the second RAT. A scenario of this sort can occur,for example, when a communication terminal moves (“roams”) to a newgeographical area.

In some embodiments that are described herein, the receiver attempts toidentify the active RAT by performing Received Signal StrengthIndication (RSSI) measurements only in the first communication channelsof the first RAT. The receiver calculates estimated RSSIs for the secondcommunication channels of the second RAT, based on the measuredfirst-RAT RSSIs. In an example embodiment, the receiver performs RSSImeasurements in GSM channels, and calculates estimated RSSIs for WCDMAchannels based on the measured GSM channel RSSIs.

Since each second (wider) communication channel typically overlapsseveral first (narrower) communication channels, the receiver is able tocompute the second RSSIs for the second communication channels based onthe first RSSIs that were measured in the first communication channels.The receiver then identifies and selects the active RAT using themeasured RSSIs of the first communication channels and the calculatedRSSIs of the second communication channels. In a typical embodiment, thereceiver selects an order of scanning at least some of the first and/orsecond communication channels based on the measured RSSIs of the firstcommunication channels and the calculated RSSIs of the secondcommunication channels. The receiver then scans the communicationchannels according to this order, so as to identify and select theactive RAT. In some embodiments, the receiver also identifies andselects one or more communication channels of the active RAT, over whichthe downlink signals are to be received.

When using the disclosed techniques, the receiver estimates the secondRSSIs for the second frequency channels without having to actuallymeasure the RSSIs according to the second RAT. As a result, the receiveris able to identify the active RAT at high speed, and the userexperiences only small latency before connecting to the activecommunication network. The reduction in latency is particularlyimportant in multi-band terminals, but the disclosed techniques areuseful in both single-band and multi-band applications.

In some embodiments, the receiver comprises separate RF receptioncircuitry for receiving the first and second RATs. When using thedisclosed techniques, the receiver may disable the reception circuitryof the second RAT during the RAT identification process. As a result,power consumption is reduced and battery time is extended.

FIG. 1 is a block diagram that schematically illustrates a wirelesscommunication terminal 20, also referred to as User Equipment (UE), inaccordance with an embodiment of the present disclosure. UE 20 maycomprise, for example, a cellular phone, a communication-enabled mobilecomputing device, a cellular adapter for a mobile computing device, orany other suitable communication terminal.

UE 20 is a multi-technology terminal, i.e., it is designed tocommunicate in accordance with two or more Radio Access Technologies(RATs). In the present context, the term RAT refers to a communicationprotocol or air interface, which defines the use of the radio resourcefor transmission. In particular, a given RAT typically specifies channelfrequencies, channel bandwidth, channel raster (i.e., frequency offsetbetween adjacent channel indices), signal waveforms and modulationschemes, and/or any other suitable signal property.

In the present example, the UE supports two RATs denoted RAT1 and RAT2,e.g., GSM and WCDMA, respectively. As such, UE 20 is designed to receivedownlink signals from RAT1 Base Stations (BSs) 24A and from RAT2 BSs24B. FIG. 1 shows both BSs 24A and BSs 24B simultaneously for the sakeof clarity. In real-life scenarios, however, the UE receives signalsaccording to only one RAT at a given time. For example, at a certaintime the UE may operate in a geographical area that is covered by RAT1BSs, and at some other time roam into another area that is covered byRAT2 BSs.

According to RAT1, BSs 24A transmit downlink signals 28A in firstcommunication channels 32A. According to RAT2, BSs 24B transmit downlinksignals 28B in second communication channels 32B. Each firstcommunication channel 32A has a first bandwidth, and each secondcommunication channel 32B has a second bandwidth, larger than the firstbandwidth. As seen in the figure, channels 32A of RAT1 overlap channels32B of RAT2, at least in a given frequency band. Although in FIG. 1 allchannels 32A and 32B are shown as if they contain signals, in real-lifescenarios each BS transmits signals only in a certain subset of itschannels, or even in a single channel.

In the present example, RAT1 comprises Global System for Mobilecommunications (GSM), and RAT2 comprises Universal MobileTelecommunications System (UMTS—also referred to as WidebandCode-Division Multiple Access—WCDMA). In accordance with presentstandards promulgated by 3GPP, each GSM channel has a bandwidth ofapproximately 200 KHz, and each WCDMA channel has a bandwidth ofapproximately 4.2 MHz. In this embodiment, both RAT1 and RAT2 have achannel raster of 200 KHz. In the present example, the WCDMA band isfully contained within the GSM band. According to the 3GPPspecifications cited above, for example, WCDMA downlink band II isdefined between 1930-1990 MHz, and the GSM PCS1900 downlink band isallocated the same band. As another example, both the WCDMA downlinkband V and the GSM850 downlink band are defined between 869-894 MHz. Inalternative embodiments, the RAT1 and RAT2 bands may overlap, fully orpartially, in any other way.

In alternative embodiments, each of RAT1 and RAT2 may comprise any othersuitable RAT having any suitable channel bandwidth and raster. Thechannel raster need not necessarily be the same in both RATs. Other RATcombinations that can be identified using the disclosed techniquescomprise, for example, GSM and CDMA, or GSM and Long-Term Evolution(LTE).

UE 20 comprises an antenna 36 for receiving downlink Radio Frequency(RF) signals from BSs 24A and 24B. A RAT1 receiver (RX) 40A receivesdownlink signals according to RAT1. A RAT2 receiver 40B receivesdownlink signals according to RAT2. Each receiver typicallydown-converts the received RF signal and applies suitable filtering andamplification to the down-converted signal, according to the applicableRAT. In an embodiment, each receiver outputs an analog signalcorresponding to a single communication channel (e.g., a single channel32A from RX 40A or a single channel 32B from RX 40B) at a given time. Insome embodiments, certain circuitry (e.g., low-noise amplificationand/or broadband down-conversion circuitry) is shared between receivers40A and 40B.

UE 20 further comprises a processor 44, also referred to as processingcircuitry, which processes the signals that are produced by receiver 40Aor 40B in order to demodulate and otherwise reconstruct the receiveddownlink signals. In particular, processor 44 determines Received SignalStrength Indications (RSSIs) on RAT1 channels 32A and RAT2 channels 32B,using methods that are described in detail further below. Processor 44comprises an RSSI estimation unit 48, which measures RSSIs on RAT1channels 32A, and calculates estimated RSSIs for RAT2 channels 32B basedon the measured RAT1 channel RSSIs. Processor 44 further comprises aRAT&channel selection unit 52, which identifies the active RAT andactive channels based on the measured RAT1 RSSIs and calculated RAT2RSSIs.

The UE configuration shown in FIG. 1 is a simplified exampleconfiguration, which is depicted solely for the sake of conceptualclarity. In alternative embodiments, any other suitable UE configurationcan be used. For example, the UE may support three or more RATs. UEelements that are not necessary for understanding the disclosedtechniques have been omitted from the figure for the sake of clarity.For example, the UE typically comprises transmission elements (not shownin the figure) for transmitting uplink signals toward the RAT1 or RAT2BSs.

The different elements of UE 20 may be implemented using dedicatedhardware, such as using one or more Application-Specific IntegratedCircuits (ASICs) and/or Field-Programmable Gate Arrays (FPGAs).Alternatively, some UE elements, and in particular processor 44 or partsthereof, may be implemented using software running on general-purposehardware, or using a combination of hardware and software elements.

Typically, processor 44 comprises a programmable processor, which isprogrammed in software to carry out the functions described herein,although it too may be implemented on dedicated hardware. The softwaremay be downloaded to the processor in electronic form, over a network,for example, or it may, alternatively or additionally, be providedand/or stored on non-transitory tangible media, such as magnetic,optical or electronic memory. In some embodiments, some or all of theelements of UE 20 may be fabricated in a chip-set.

Typically, only one RAT is active in a given frequency band, e.g., asdecided by a service provider in a given geographical area. In somescenarios, UE 20 seeks network coverage in order to provide the end userservice to some extent, but has no a-priori information as to whetherthe active RAT is RAT1 or RAT2. Such a scenario occurs, for example,when UE 20 initially attempts to join a communication network. Forexample, the UE may be switched on within the coverage area of a givennetwork, or it may “roam” to another geographical area.

In some embodiments, processor 44 carries out a process thatautomatically identifies the active RAT, and possibly one or more activechannels of this RAT. In an embodiment, RSSI estimation unit 48processor 44 measures respective first RSSIs in channels 32A of RAT1.Each first RSSI indicates the received signal strength that was measuredin a respective channel 32A of RAT1. Using the measured RAT1 RSSIs, unit48 computes second RSSIs for channels 32B of RAT2. Each second RSSIestimates the received signal strength in a respective channel 32B ofRAT2.

In an example embodiment, unit 48 estimates the RAT2 RSSI of a certainchannel 32B by summing the RAT1 RSSIs over the RAT1 channels 32A thatare contained in that channel 32B. (In some embodiments, the RSSI valuesare given on a logarithmic scale, for example in dBm. The summation ofRSSI values in these embodiments refers to summing the linear signalstrength values and converting the sum back to the logarithmic scale.)As seen in FIG. 1, each channel 32B overlaps several channels 32A. Inthe GSM/WCDMA example described above, each WCDMA channel overlapsapproximately 4.2 MHz/200 KHz=21 GSM channels. In an embodiment, unit 48estimates the RSSI of a given WCDMA channel by summing the twenty-oneRSSIs that were measured in the twenty-one GSM channels that overlapthis WCDMA channel.

In some embodiments, unit 48 multiplies the measured RAT1 RSSIs bycertain weights before summing them, to produce an estimated RAT2 RSSI.In an example embodiment, unit 48 assigns higher weights to the RAT1RSSIs of the RAT1 channels 32A that are located in the middle of theRAT2 channel 32B in question, and lower weights to the RAT1 RSSIs of theRAT1 channels 32A that are on the edges of this RAT2 channel 32B.

In another embodiment, unit 48 sums the RAT1 RSSIs of the RAT1 channels32A contained in a given RAT2 channel 32B, with or without weighting.Unit 48 then scales the summation result by a certain scaling factor, toproduce the estimated RAT2 RSSI. The scaling factor may depend, forexample, on the modulation pulse shapes (which generally correspond tothe respective channel filter shapes) of RAT1 and RAT2. Furtheralternatively, unit 48 in processor 44 may compute the estimated RAT2RSSIs for channels 32B based on the measured RAT1 RSSIs of channels 32Ausing any other suitable method.

In some embodiments, RAT&channel selection unit 52 in processor 44identifies the active RAT using the measured RAT1 RSSIs and calculatedRAT2 RSSIs, which were produced by unit 48. In an example embodiment,unit 52 searches the calculated RSSIs for a predefined channel RSSIpattern. For example, RAT2 channels (32B) often have a distinct RSSIvalue pattern spread over 4.2 MHz. Finding a similar pattern in thecalculated RAT2 RSSIs might strongly indicate that RAT2 is the activeRAT. In some embodiments, unit 52 may regard the RAT that ischaracterizes by the highest RSSIs (measured or calculated) as theactive RAT. In an embodiment, the highest RSSIs are also required toexceed a certain RSSI threshold.

In some embodiments, unit 52 defines an order of scanning at least someof the RAT1 and/or RAT2 channels based on the measured RAT1 RSSIs andthe calculated RAT2 RSSIs. In an example embodiment, the order scans theRAT1 and RAT2 channels in descending order of RSSI. The receiver thenscans the communication channels according to this order, so as toidentify the active RAT. In an embodiment, scanning the channels in theabove-described order also enables the receiver to find a particularchannel for communication using the active RAT.

Further aspects of RAT selection are addressed in 3GPP TechnicalSpecification TS 23.122, entitled “3^(rd) Generation PartnershipProject—Technical Specification Group Core Network andTerminals—Non-Access-Stratum (NAS) Functions Related to Mobile Station(MS) in Idle Mode (Release 8),” version 8.9.0, March, 2010, section 4,and in 3GPP Technical Specification TS 25.304, entitled “3^(rd)Generation Partnership Project—Technical Specification Group RadioAccess Network—User Equipment (UE) Procedures in Idle Mode andProcedures for Cell Reselection in Connected Mode (Release 8),” version8.8.0, December, 2009, section 5, which are incorporated herein byreference.

In some embodiments, unit 52 also selects one or more active channels ofthe active RAT, in which downlink signals are to be received at the UE.In an example embodiment, after identifying the active RAT, unit 52selects the channels of that RAT that have the strongest RSSIs.

It is noted that estimation of the RAT2 RSSIs is performed withoutactually measuring the RSSIs on channels 32B according to RAT2. The onlyactual measurements are the RAT1 RSSI measurements carried out overchannels 32A of RAT1. In the present GSM/WCDMA example, the disclosedtechniques reduce the network identification time by several seconds, incomparison with direct measurements of the RAT2 RSSIs.

In some embodiments, processor 44 deactivates RAT2 receiver 40B duringthe RAT identification process. Deactivation of this sort is possiblebecause the identification process uses only the signals produced byRAT1 receiver 40A, and not the signals produced by RAT2 receiver 40B.This technique reduces the power consumption of the UE, and thereforeextends its standby time.

FIG. 2 is a flow chart that schematically illustrates a method forcommunication in wireless communication terminal 20, in accordance withan embodiment of the present disclosure. The method begins with unit 48in processor 44 measuring respective RSSIs in channels 32A of RAT1, at ameasurement operation 60. In the GSM/WCDMA example embodiment, unit 48measures the RSSIs in the GSM channels.

Based on the measured RAT1 RSSIs, unit 48 calculates respective RAT2RSSIs for channels 32B of RAT2, at a calculation operation 64. In theGSM/WCDMA example embodiment, unit 48 calculates a respective RSSI foreach WCDMA channel, based on the measured RSSIs of the GSM channels thatoverlap this WCDMA channel.

Based on the measured GSM RSSIs and calculated WCDMA RSSIs, unit 52 inprocessor 44 identifies the active RAT, at an identification operation68. In the GSM/WCDMA example embodiment, unit 52 identifies whether theactive RAT is GSM or WCDMA. In an embodiment, unit 52 also identifiesthe actual channels of the active RAT in which signals are received bythe UE. In an embodiment, once processor 44 has identified the activeRAT, it identifies the active channels, which corresponds to BSs of thisRAT that are received by the UE.

The UE then begins to communicate using the identified active RAT,Typically, the UE communicates using one or more of the channels thatwere identified as active. In an example embodiment, processor 44selects one or more BSs that are candidates for registration by the UE,and attempts to lock on the BS having the strongest signal.

In some embodiments, processor 44 measures and represents the RAT1 RSSIsover a wide dynamic range, in order to enable successful calculation ofthe RAT2 RSSIs. Consider, for example, a WCDMA/GSM UE. In thisapplication, measuring and representing the GSM RSSIs down to a minimumsensitivity of −105 dBm is typically sufficient for identifying activeGSM channels. If such a sensitivity were used for calculating WCDMARSSIs, however, the WCDMA RSSIs would have a minimum sensitivity of−105+13=−92 dBm. (The 13 dB factor originates from the summation overtwenty-one GSM channels to produce each calculated WCDMA RSSI.) Thissensitivity is sometimes insufficient for accurate estimation of theWCDMA RSSIs—Weak WCDMA carriers may be indistinguishable from noise withthis sort of sensitivity. In other words, a sensitivity of this sortwould create a relatively high RSSI floor in the WCDMA RSSI calculation,a floor that would make weak WCDMA channels indistinguishable fromnoise. Therefore, in an embodiment, processor 44 measures and representsthe GSM RSSIs at an improved minimum sensitivity of −110 dBm. As aresult, the WCDMA RSSIs can be estimated at a sensitivity of −97 dBm,which is generally sufficient.

It is noted that the embodiments described above are cited by way ofexample, and that the present invention is not limited to what has beenparticularly shown and described hereinabove. Rather, the scope of thepresent invention includes both combinations and sub-combinations of thevarious features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

The invention claimed is:
 1. A method, comprising: receiving signals using a receiver that supports, in a given frequency band, a first set of first communication channels each having a first channel bandwidth, and a second set of second communication channels each having a second channel bandwidth that is larger than the first channel bandwidth; measuring first Received Signal Strength Indications (RSSIs) for the respective first communication channels; computing second RSSIs for the respective second communication channels, by applying to a plurality of the first RSSIs an arithmetic computation comprising calculating a second RSSI for a respective second communication channel by summing the first RSSIs measured on a subset of the first communication channels overlapping the second communication channel, and multiplying a sum of the first RSSIs in the subset by a factor that depends on respective first and second channel filter shapes of the first and second communication channels; and selecting from among the first and second sets, using the measured first RSSIs and the computed second RSSIs, at least one of the communication channels over which to receive the signals at the receiver.
 2. The method according to claim 1, wherein measuring the first RSSIs comprises measuring signal strengths of the signals received over at least one of the first communication channels in accordance with a first Radio Access Technology (RAT), and wherein the second communication channels correspond to a second RAT, different from the first RAT.
 3. The method according to claim 2, wherein only one of the first and second RATs is active when the first RSSIs are measured, and wherein selecting the at least one of the communication channels comprises identifying the active RAT.
 4. The method according to claim 2, comprising, in response to identifying the active RAT, initiating communication with a base station of the identified active RAT.
 5. The method according to claim 2, wherein measuring the signal strengths comprises receiving the signals of a Global System for Mobile communication (GSM) RAT, and wherein computing the second RSSIs comprises computing the second RSSIs in accordance with a Universal Mobile Telecommunications System (UMTS) RAT.
 6. The method according to claim 1, wherein summing the first RSSIs comprises assigning respective weights to the first RSSIs in the subset, and summing the weighted first RSSIs.
 7. The method according to claim 1, wherein the receiver includes first and second reception circuitry for receiving the first and second communication channels, respectively, and comprising deactivating the second reception circuitry during measurement of the first RSSIs.
 8. A receiver, comprising: reception circuitry, which is configured to receive signals in a given frequency band in a first set of first communication channels each having a first channel bandwidth, and in a second set of second communication channels each having a second channel bandwidth that is larger than the first channel bandwidth; and processing circuitry, which is configured to measure first Received Signal Strength Indications (RSSIs) for the respective first communication channels, to compute second RSSIs for the respective second communication channels by applying to a plurality of the first RSSIs an arithmetic computation comprising calculating a second RSSI for a respective second communication channel by summing the first RSSIs measured on a subset of the first communication channels overlapping the second communication channel and multiplying a sum of the first RSSIs in the subset by a factor that depends on respective first and second channel filter shapes of the first and second communication channels, and to select from among the first and second sets, using the measured first RSSIs and the computed second RSSIs, at least one of the communication channels over which to receive the signals by the reception circuitry.
 9. The receiver according to claim 8, wherein the reception circuitry is configured to receive the signals in at least one of the first communication channels in accordance with a first Radio Access Technology (RAT), and wherein the second RSSIs second communication channels correspond to a second RAT, different from the first RAT.
 10. The receiver according to claim 9, wherein only one of the first and second RATs is active when the first RSSIs are measured, and wherein the processing circuitry is configured to identify the active RAT.
 11. The receiver according to claim 10, wherein the processing circuitry is configured to initiate communication with a base station of the identified active RAT in response to identifying the active RAT.
 12. The receiver according to claim 9, wherein the processing circuitry is configured to measure the first RSSIs by measuring the signals of a Global System for Mobile communication (GSM) RAT, and to compute the second RSSIs in accordance with a Universal Mobile Telecommunications System (UMTS) RAT.
 13. The receiver according to claim 8, wherein the processing circuitry is configured to assign respective weights to the first RSSIs in the subset, and to sum the weighted first RSSIs.
 14. The receiver according to claim 8, wherein the reception circuitry comprises first and second circuitry for receiving the first and second communication channels, respectively, and wherein the processing circuitry is configured to deactivate the second circuitry during measurement of the first RSSIs.
 15. A mobile communication terminal comprising the receiver of claim
 8. 16. A chipset for processing signals in a mobile communication terminal, comprising the receiver of claim
 8. 